For NFT, the nutrient solution is continuously flowing over the roots. This is accomplished using gravity. The grow tray is placed at an angle to allow the water to flow down towards the drain pipe, and new solution is constantly being pumped into the high end of the tube. NFT is an active system, meaning it relies on moving parts to work. The nutrient solution flows in a thin film over the roots, ensuring that they are watered and fed but not completely soaked. The thin film ensures that the upper part of the roots will remain dry and have access to oxygen in the air.